From: Alan Mackenzie <acm@muc.de>
To: emacs-devel@gnu.org
Subject: Re: Scrolling xdisp.c. Room for optimisation in syntax.c/CC Mode.
Date: Sat, 18 Oct 2014 20:28:39 +0000 [thread overview]
Message-ID: <20141018202839.GB5924@acm.acm> (raw)
In-Reply-To: <20141018181937.GA5924@acm.acm>
On Sat, Oct 18, 2014 at 06:19:38PM +0000, Alan Mackenzie wrote:
> Hi, Emacs.
> I've measured the time Emacs takes to scroll a large C file, and how much
> of this is due to the inefficiency in backwards `scan-lists's when
> comments contain unbalanced string characters (with
> open-paren-in-column-0-is-defun-start nil).
[ ... ]
> On my set up, a Linux virtual terminal with a window 65 lines high, I get
> the following results:
> no-odd-xdisp.c: 492 scrolls, total time = 42.2749125957489s
> xdisp.c: 492 scrolls, total time = 69.40998315811157s.
> 69.4100 / 42.2749 = 1.642. The original thus takes 64% longer (on
> average) for a backward scroll operation.
I forgot to mention that this was on Emacs 24.3, with full .emacs loaded,
and with an up-to-date stand-alone CC Mode.
> It would seem worthwhile to consider optimising the code to eliminate
> this 64%. Two possibilities suggest themselves: (i) in syntax.c, by
> making use of the syntax-ppss cache (or similar); (ii) In CC Mode, by
> setting syntax-table text properties on unbalanced string quotes.
I've just repeated the measurement on the Emacs trunk, with emacs -Q. I
now get these results:
no-odd-xdisp.c: 500 scrolls, total time = 104.21487808227539s.
xdisp.c: 500 scrolls, total time = 167.73530864715576s.
I don't know why there are more scroll operations needed. But the fact
that scrolling is taking two and a half times longer in the trunk than in
24..3 is noteworthy, and possibly disturbing. I'm think I compiled both
version with the same optimisation level, etc.
> --
> Alan Mackenzie (Nuremberg, Germany).
next prev parent reply other threads:[~2014-10-18 20:28 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-18 18:19 Scrolling xdisp.c. Room for optimisation in syntax.c/CC Mode Alan Mackenzie
2014-10-18 20:28 ` Alan Mackenzie [this message]
2014-10-19 16:37 ` Ulrich Mueller
2014-10-19 17:49 ` Eli Zaretskii
2014-10-19 18:05 ` Ulrich Mueller
2014-10-20 1:41 ` Stefan Monnier
2014-10-20 7:24 ` Ulrich Mueller
2014-10-20 15:45 ` Stefan Monnier
2014-10-20 16:55 ` Ulrich Mueller
2014-10-20 7:29 ` martin rudalics
2014-10-20 11:47 ` Alan Mackenzie
2014-10-20 12:05 ` martin rudalics
2014-10-20 12:22 ` Óscar Fuentes
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